There is an increasing desire to find more environmentally friendly fuels for cars than pure gasoline. Among the alternatives considered are alcohols such as ethanol and methanol, and blends of gasoline and alcohol in varying proportions.
Flexible Fuel Vehicles are automobiles or light trucks that are able to operate on multiple fuel blends. The usable fuels include regular gasoline as well as several alternative fuels such as M-85 (85% Methanol & 15% gasoline), E-85 (85% Ethanol & 15% gasoline) or pure mixed alcohol.
To be able to operate on different fuel blends, flexible fuel vehicles comprise an engine control unit, which among other things, is arranged to run a fuel adaptation algorithm. This processor detects what fuel blend is being used and automatically adjusts the engine's ignition timing and air/fuel mixture ratios accordingly by means of the fuel adaptation algorithm. The engine control unit adjusts the engine's optimum performance for any ratio of gasoline to fuel alcohol.
After each refuelling event the new ethanol or methanol rate must be detected and the control unit must be adapted to the new rate. This adaptation must be fully performed in order to avoid engine breakdown caused by high temperature at high loads.
Lambda control is used to optimize the air fuel ratio provided to the engine. A lambda sensor monitors the oxygen differential between the exhaust pipe and the atmosphere. This value is used to adjust the air fuel ratio in order to get an optimal exhaust gas catalyst conversion efficiency.
The fuel adaptation algorithms known in the art can only be executed when the vehicle's lambda closed loop controller is active. The lambda closed loop controller can only be active in a part of the engine's operating range, which is limited both by engine speed and by load. Outside this area the fuelling of the engine must be accurately pre-controlled to avoid potential engine damage due to exceeded limits for the engine hardware and catalyst (exhaust gas over temperatures etc.). If a fuel adaptation has not been executed and the present ethanol rate has not yet been securely detected the speed and load has to be limited to where the lambda closed loop controller can be active. This leads to a considerable performance loss when the engine is working outside of this part of the working area. Such performance losses are experienced as highly unsatisfactory by the driver.